1. Field of the Invention
The present invention relates to a process for halogenating 6-hydroxy picoline derivatives in the 3-position. The process is accomplished by allowing a 6-halo picoline derivative to stand in an aqueous mineral acid solution for a sufficient period to replace the halo substituent with a hydroxy substituent, and halogenating the aqueous mineral acid solution of 6-hydroxy picoline derivative to produce the corresponding 3-halo 6-hydroxy picoline derivative.
2. Description of the Prior Art
In current technology, as exemplified by U.S. Pat. No. 4,217,185, the process arrives at the product 3,6-dichloropicolinic acid, which is known as Lontrel.RTM., through a reduction process comprising passing a D.C. current to a cathode from an anode through an aqueous basic solution of tetrachloro-2-picolinic acid in order to obtain the products 3,4,6- and 3,5,6-tricholoro-2-picolinic acids, which can further be reduced to 3,6-dichloro picolinic acid.
U.S. Pat. No. 4,087,431 pertains to a process for preparing 3,6-dichloropicolinic acid by (a) reacting 3,5,6-trichloro-4-hydrazino-picolinic acid with a basic reagent at temperatures of from 60.degree. C. to reflux for a period of one-half to three hours; (b) acidifying the mixture with a mineral acid to a pH of about 1, and recovering the product.
U.S. Pat. No. 4,334,074 discloses a process for recovering 3,6-dichloro picolinic acid from basic aqueous solution by acidification with HCl and a flocculant, separating said acid, extracting the unprecipitated acid from the mother liquor with a solvent, and stripping the extracted acid from the solvent with a separate portion of the basic feed solution.